Hello I was making a railroad and it will be fun to make train crashes with it, but with a dozen car train crashes into a another train almost all the cars go flying
You need create a script that detects when the train crashes to stop whatever script/bodyvelocity that you are applying to the trains. That way they will not float away as they are currently doing so.
If you wish to get fancy with it you could even attempt to make your own crash animation (use bodygryo or something to tilt the train off to a specific side etc)